In general, vertical cavity surface emitting lasers (VCSEL) are constructed by providing a substrate with very smooth surface. A first stack of mirrors is then grown on the surface by semiconductor manufacturing techniques. An active area is grown on the upper surface of the first mirror stack and a second mirror stack is grown on the upper surface of the active area. Generally, metal contacts formed of an easily deposited metal, such as gold, titanium, tungsten, platinum, or the like, are provided. In general, one metal contact is provided on the surface of the first (lower) mirror stack and a second metal contact on the upper surface of the second mirror stack. The problem is that these metals are very expensive and add greatly to the ultimate cost of the device.
The major problems that occur are to contain the lasing, or optical mode to a lowest order mode and to contain current flow to approximately the volume of the VCSEL in which lasing is occurring. Higher order lasing and extraneous flow of current outside the lasing area produces heat in the VCSEL and causes a substantial loss of power. One method utilized to contain current flow to a desired area is to provide implants of materials which reduce or prevent current flow in the implanted area, or produce reverse biased diodes. The problem with this solution is that implants require a very high acceleration voltage, in some instances 400 kV or more, and are easily disbursed by subsequent operations.